The present invention relates generally to battery structures and deals more particularly with a flexible battery structure.
The advent of portable electronic devices such as laptop computers, mobile communication devices and personal digital assistants, for example, have created a demand for lightweight, high capacity batteries. Typical battery structures are somewhat rigid and typically are encased in a metallic can or other such rigid material to protect the battery and/or apply pressure to the battery components to create the necessary chemical reaction to produce electron flow. The use of such materials has limited the practical reduction in battery size and application of such batteries. Additionally, such battery materials could not accommodate applications wherein the battery structure encountered frequent flexing and bending such as in clothing apparel applications or wrist-worn products.
It was thought that lithium polymer batteries, which use a foil package made of a lamination of an aluminum layer between two plastic layers, would provide the desired flexibility for such applications. In reality, the aluminum is not able to withstand many bendings and thus does not provide the desired flexibility and reliability. In addition, the plastic lamination is susceptible to water impregnation, which reacts with the lithium to cause the battery to fail in a relatively short time.
A further disadvantage of such polymer batteries is the requirement that the electrode tabs must extend from within the plastic packaging to permit contact with an external electrical circuit with which the battery is used. It is difficult to completely seal the space through which the electrode tabs extend, which leads to an additional possible entry point for water impregnation.
Therefore, it is an object of the present invention to provide a flexible battery structure that can withstand repeated bending and flexing.
It is a further object of the present invention to provide a flexible battery structure that has a thinner profile thickness than equivalent conventional power density battery structures.
The present invention substantially obviates, if not entirely eliminates, the disadvantages of utilizing lithium polymer and other such batteries having foil packages made of a lamination of aluminum and plastic layers by providing a polymer battery wherein the outer packaging is eliminated entirely to reduce the thickness of the battery and allow flexing and bending of the battery structure.
In one aspect of the present invention, a flexible battery structure comprises a first flexible substrate having an inner surface face and an outer surface face defining a cathode; a layer of cathode active material adjacent to the inner surface face of the cathode substrate; a layer of electrolyte adjacent to the layer of cathode active material; a layer of anode active material adjacent to the electrolyte layer; a second flexible substrate having an inner surface and an outer surface face defining an anode wherein the anode inner surface is adjacent to the anode active material layer; and means for sealing the stack of layers formed between the first and second substrates.
Preferably, the cathode substrate and anode substrate have surface face areas larger than the stacked layers to define a marginal peripheral seam to sandwich the stacked layers.
Preferably, the marginal peripheral seam further comprises overlapping portions of each of the cathode substrate and anode substrate with respect to one another in a spaced relationship to prevent an electrical short circuit between said cathode substrate and said anode substrate.
Preferably, the marginal peripheral seam is hermetically sealed.
Preferably, the hermetic seal is comprised of a water-resistant composite material inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam.
Preferably, the cathode and anode substrates are made of a metal foil wherein the cathode substrate is copper and the anode substrate is aluminum.
Preferably, the cathode outer surface face and the anode outer surface face define the exterior surfaces of the battery structure.
Preferably, the cathode outer surface face comprises the positive polarity connection lead and the anode outer surface face comprises the negative polarity connection lead.
Preferably, the layer of electrolyte comprises means for separating the cathode substrate and the anode substrate.
In a further aspect of the invention, one or more glass balls are inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam to hermetically seal the seam between the cathode and anode substrates. Preferably, a non-electrically conductive, water-resistant composite material is inserted between the overlapping portions of the cathode and anode substrates defining the marginal peripheral seam.
Other features and advantages of the present invention will become more apparent from an understanding of the following detailed description of presently preferred embodiments of the invention when considered in conjunction with the accompanying drawings.